1. Field of the Invention
The present invention relates to a system and a method for dynamically controlling storage device access duty cycle.
2. Background Art
Data storage devices (e.g., disk drives, tape drives, and the like) have advertised reliability numbers (e.g., mean time between failures, MTBF) that are based on several external factors. MTBF for a storage device is generally calculated at a given duty cycle, i.e., the percentage of time the storage device is performing an access (e.g., reading, writing, verifying data, etc.).
Reliability is an important factor in customer satisfaction with data storage devices. One of the major factors in the determination of storage device reliability is the duty cycle of the storage device. The duty cycle can be a particularly important factor in the MTBF of inexpensive storage devices such as Advanced Technology Attachment (ATA) disk drives. The reliability MTBF projections are substantially reduced when duty cycles are above the levels that are specified by the storage device manufacturer. MTBF can vary non-linearly with increased duty cycle. In many data storage subsystem implementations, the subsystem has minimal control at best over input/output (IO) patterns that are received from host devices. Thus, actual MTBFs for conventional storage device approaches can be substantially less than manufacturer reliability projections (i.e., the storage devices can be less reliable than projected) and customer satisfaction can be negatively affected.
Further, in redundant powered data storage systems (systems that generally are implemented with two separate power supplies, so-called 2N supply systems), each power supply is generally configured having capacity sufficient to support the entire data storage system load. For example, when one of the power supplies breaks down or is taken off line for upgrades, repair and the like, the remaining power supply is sized such that the data storage system can remain substantially fully functional.
In a typical data storage system, each power supply is generally configured to support maximum electrical current loads at a number of substantially constant voltage levels (e.g., 5 V and 12 V). However, some data storage system components (e.g., drives) in a multiple data storage device system have a high current load at a first voltage level (e.g., a 5 V level), and other data storage system components have a high current load at another voltage level (e.g., a 12 V level). As such, each power supply is configured to support the maximum electrical current load at all of the voltage levels. Because data storage systems are not typically implemented with data storage devices that all present all of the maximum current loads, the conventional system are implemented with excess current and power capacity and the related cost, weight and size deficiencies.
Yet further, the data storage system power supply is to be specified to ensure adequate power to meet customer power demands (i.e., loads). Using conventional approaches, the sum of the worst case power consumption for all of the system components is used to ensure that each power supply can support the worst case load. The worst case load includes worst case activity on the storage device drives, whether the worst cast is 100% sequential read operations, 100% random read/write operations, or any other worst case operation including a worst case per power supply output.
Under typical operating conditions, the worst case load is rarely encountered. Storage system drive operation is typically more idle than active. Conventional approaches to storage systems generally yield over-rated power supplies and corresponding increased cost, size and weight. In one circumstance, a power supply system that is rated for worst case operation is justified, that is, when the data storage system is known to encounter all worst case power draws and worst case drive activity. However, for many other data storage systems, conventional approaches yield over-rated power supplies.
Thus there exists an opportunity and need for an improved system and method for a storage device that provides dynamic control of the duty cycle of accesses to and from the storage device.